How many RC's we have will depend on how well 8.0-RC1 does. At the moment only one more RC is on the schedule but odds are fairly high we will wind up inserting at least one more RC. Between BETA4 and RC1 a lot of work has gone into IPv6 issues as well as many other issues that have been brought up from the public testing. And a patch set was committed by the people who handle porting ZFS to FreeBSD that they felt makes ZFS production-ready.